This application claims priority from Taiwanese application Serial No. 089106924, filed on Apr. 13, 2000.
1. Field of the Invention
The present invention relates generally to a computer motherboard for supporting various memories, and more particularly to a computer motherboard for supporting single data rate (SDR) dynamic random access memory (DRAM) and double data rate (DDR) DRAM.
2. Description of the Related Art
As the technologies improve day after day, the personal computer-related sciences also drastically improve. For memory storing programs or data in a computer system, the system memory is most often configured onboard. The memory of this sort comprises integrated circuits (ICs), which is also known as main memory.
FIG. 1 is a schematic block diagram of personal computer in the prior art. In FIG. 1, motherboard 100 comprises a central processing unit (CPU) 101, a north bridge (NB) 102 and a DRAM 103. CPU 101 is in charge of computing, processing, controlling and other significant tasks. North bridge 102 is an important device for system demand to high speed processing ability and good performance. DRAM is accessed by CPU, and programs should be placed in the DRAM in order to execute them. DRAM is provided with the advantages of simple structure, high data capacity and low cost so that it is widely used in personal computer system nowadays.
Today memory is made up of several DRAM chips and becomes a memory module called dual inline memory module (hereinafter referred to DIMM). In this specification, both of SDR DIMM and DDR DIMM are constructed of DIMM type memory modules, wherein SDR DIMM is a kind of DIMM made up of several DRAM chips supporting SDR communication, and DDR DIMM is a kind of DIMM made up of several DRAM chips supporting DDR communication, similarly. In view of memory reference clocks, the memories are separated into SDR type and DDR type. FIG. 2 is a timing chart of reference clocks of SDR DIMM and DDR DIMM under the same operating frequency. As shown in FIG. 2, the SDR reference clock is composed of a single clock, but the DDR reference clock is composed of two clocks whose frequencies are identical and whose phases have difference in 180 degrees with each other. For SDR and DDR communication, data transmission occurs while the reference clock reaches the rising edge thereof. In FIG. 2, symbol xe2x80x9c↑xe2x80x9d represents the time at which data is output. During one clock cycle, SDR memory has one clock rising edge, that is, it has one data output period. During the same cycle, DDR memory has two clock rising edges so it has two data output periods. It is obvious that DDR DIMM operates more efficiently than SDR DIMM. However, SDR DIMM is popular in market these days because of its lower price. Table I shows the transmission bandwidths of SDR DIMM and DDR DIMM.
In Table I, xe2x80x9cMBpsxe2x80x9d represents mega bytes per second, and xe2x80x9cGBpsxe2x80x9d represents giga bytes per second. For instance, SDR66 is a kind of SDR DIMM, operating under 66 MHz frequency, and has 528 MBps transmission bandwidth. As shown in the foregoing Table, under the same operating frequency the transmission bandwidth of DDR memory is better than that of SDR memory.
FIG. 3A is a schematic block diagram showing a conventional motherboard using DDR DIMMs. Motherboard 300 includes a north bridge 301 and two DDR DIMMs lots 302, 303. Certainly, practical circuitry of the motherboard is not that simple as shown in FIG. 3A, so FIG. 3A is merely used to illustrate some circuitries related to memory control or transmission. While a user utilizes DDR DIMMs, DDR DIMM 304, 305 must be inserted into DDR DIMM slots 302, 303.
DDR DIMM is driven by 2.5V power. As shown in FIG. 3A, while applying DDR DIMM on motherboard, there is a serial resistor RS between north bridge 301 and DDR DIMM slot. The resistance of resistor RS is generally 22 ohm. In addition, there is another resistor, termination resistor RT, coupled to DDR DIMM slot. The other terminal of termination resistor RT is coupled to termination voltage VTT. The resistance of termination resistor RT is generally 25 ohm. Termination voltage VTT is ordinarily 1.25V, which is provided from motherboard. To let the logic levels of two individual devices, north bridge and DDR DIMM, respectively reach the predetermined logic ranges, to let the whole circuitry be operated more stably and to diminish the interactive power consumption between these two devices, serial resistor RS, termination resistor RT and termination voltage VTT are applied to the connection of the motherboard.
FIG. 3B is a schematic block diagram showing a conventional motherboard using SDR DIMM. Motherboard 300 includes a north bridge 301 and two SDR DIMM slots 306, 307. Certainly, practical circuitry of the motherboard is not that simple as shown in FIG. 3B, so FIG. 3B is merely used to illustrate some circuitries related to memory control or transmission. When a user utilizes SDR DIMM, SDR DIMM 308, 309 must be inserted into SDR DIMM slots 306, 307.
SDR DIMM is driven by 3.3V power. As shown in FIG. 3B, when applying SDR DIMM on motherboard, there is no serial resistor between north bridge 301 and SDR DIMM slot, and there is no termination resistor coupled to SDR DIMM slot.
Although SDR DIMM is still popular in memory market now, according to conventional experience, new memory product with higher price but having better performance will replace it due to the technical improvement. As for DRAM market, it would be anticipated that DRAM application transits from SDR DIMM to DDR DIMM.
During the transition stage from SDR to DDR, most users request that designed motherboard supports both of SDR DIMM and DDR DIMM in the meantime. Hence, users can utilize SDR DIMM on that motherboard. As DDR DIMM becomes cheaper and users want to change SDR DIMM with DDR DIMM, they can also apply DDR DIMM on the same motherboard without additional expense to replace that motherboard with a new one. Furthermore, the settings on how to use SDR/DDR DIMM are simpler; it is more convenient for users. It would, therefore, not cause users much trouble during the replacement of SDR DIMM and DDR DIMM.
It is therefore an object of the invention to provide a computer motherboard capable of supporting at least two kinds of memory products and easy setting. Applying the invention in a computer motherboard, users can easily, freely select one type from those memory products to use without complicated settings.
According to an object of the invention, a computer motherboard for selectively using one of SDR DIMM and DDR DIMM by a dummy card is disclosed. The computer motherboard comprises a chip, a SDR DIMM slot, a serial resistor and at least two DDR DIMM slots. The SDR DIMM slot is coupled to the chipset for holding a SDR DIMM. The serial resistor is coupled to the SDR DIMM slot. The DDR DIMM slots are coupled to the resistor for holding one DDR DIMM, respectively. When a DDR DIMM is inserted into one of these DDR DIMM slots, the dummy card should be inserted into another one of the DDR DIMM slots in the meantime.
According to another object of the invention, the invention provides a computer motherboard for selectively using one of SDR DIMM and DDR DIMM by a dummy card. The computer motherboard comprises a chipset, a serial resistor, a SDR DIMM slot and at least two DDR DIMM slots. The serial resistor is coupled to the chipset when the SDR DIMM slot for holding a SDR DIMM is coupled to the serial resistor. The DDR DIMM slots for respectively holding one DDR DIMM are coupled to the SDR DIMM slot. The dummy card is inserted into one of the DDR DIMM slots while a DDR DIMM is inserted into another one of the DDR DIMM slots.
According to one object of the invention, the invention provides a computer motherboard for selectively using one type of SDR DIMM and DDR DIMM by a dummy card. The computer motherboard comprises a chipset, a serial resistor, at least two DDR DIMM slots and a SDR DIMM slot. The serial resistor is coupled to the chipset. The DDR DIMM slots for respectively holding a DDR DIMM is coupled to the serial resistor. The SDR DIMM slot for holding a SDR DIMM is coupled to the DDR DIMM slots. When a DDR DIMM is inserted into one of the DDR DIMM slots, the dummy card is inserted into another one of the DDR DIMM slots.
According to further object of the invention, the invention provides a computer motherboard for selectively using one of SDR DIMM and DDR DIMM by a dummy card. The computer motherboard comprises a chipset, a serial resistor, a SDR DIMM slot and a DDR DIMM slot. The serial resistor is coupled to the chipset. The SDR DIMM slot for holding a SDR DIMM is coupled to the serial resistor. The DDR DIMM slot for holding a DDR DIMM is coupled to the SDR DIMM slot. When a DDR DIMM is inserted into the DDR DIMM slot, the dummy card is inserted into the SDR DIMM slot.
According to one object of the invention, a computer motherboard is provided for selectively using one of SDR DIMM and DDR DIMM by a dummy card. The computer motherboard comprises a chipset, a serial resistor, a DDR DIMM slot and a SDR DIMM slot. The serial resistor is coupled to the chipset. The DDR DIMM slot for holding a DDR DIMM is coupled to the serial resistor. The SDR DIMM slot for holding a SDR DIMM is coupled to the DDR DIMM slot. When a DDR DIMM is inserted into the DDR DIMM slot, the dummy card is inserted into the SDR DIMM slot.